A hobgoblin legion camp, or "castellum goblinus", is a four-sided, walled structure designed to neatly hold the hundreds of tents and semi-permanent structures needed for hobgoblin legions on the war-march.
This particular camp is located in the Southern Badlands near the edge of the Hyrcanian Desert, and appears to be a permanent or semi-permanent structure, as opposed to a temporary one. The palisade walls and trenches around the fort appear to be reinforced, and small lookout towers have been erected several miles from the fort.
The troops from this camp amassed their strength for several months, and at the end of Leafall took to the warpath, lead by the imposing hobgoblin known as The Praetor. The citizens of Willowdale prepared their best defense and won the battle, though both sides took heavy losses.
While the majority of the hobgoblins were killed or routed during the war, leaving this camp mostly abandoned, a small group of Centurion survivors returned and continued to live here. They seemed resigned to eking out a living in the ruins of their camp, rather than risk unknown lands to the north or an encounter with the Cinder Man on their way back south. After being informed that the Cinder Man was roving the desert nearby and was reasonably likely to find them, the remaining hobgoblins decided to move once they were told of the abandoned yet servicable base in the Farsang Fens they could use, leaving this camp empty.
Most castellum follow a rigid, unchanging layout, drilled into hobgoblins who must make and break camp each and every day while under march.
Outer defenses include: a 10-foot palisade wall, with small lookout posts and gates at every entrance, a 5-foot trench dug out before the wall with sharpened sticks and rocks lining the sides to prevent easy movement, and a series of watch towers beyond the perimeter of the outer wall.
The interior of the camp is split by a main road into the barracks and storage tents for the legionnaires and the auxiliares (the non-combatants), and into the specialized tents for commanders, siege weapons, elite soldiers, slaves, and warbeasts.
Alejandra has pointed out that the highly standardized layout of each camp is a tactical weakness, and her own military's familiarity with the design has unveiled numerous means of crippling or completely destroying the camp from within. Whether it comes from "breaking the limbs" (using fire attacks to destroy barracks and storage tents, freeing slaves, or loosing warbeasts) or "removing the head" (destroying the central standard used for organization, attacking the leader's tent), the use of even basic tactics has allowed much smaller forces to overcome the hobgoblins' numerical advantage.